1. Field of the Invention
The present invention relates to an apparatus for combining pacing and cardioverting functions in a single implanted device, and more particularly to interface and protection circuitry for use in conjunction with defibrillator systems or combined defibrillator-pacer systems.
2. Description of the Prior Art
In recent years, substantial progress has been made in the development of defibrillation techniques for providing an effective medical response to various heart disorders or arrhythmias. The types of contemplated disorders or arrhythmias are typically treated by use of defibrillators and/or pacers, and typical arrangements also employ electrocardiograph (ECG) amplifiers for sensing heart activity and providing amplified electrical signals corresponding thereto and/or for synchronizing the employed technique with the heart activity.
A problem arises in the use of defibrillation circuitry in conjunction with ECG amplifiers, in that the sensitive circuitry of the ECG amplifier must be protected from defibrillation pulses. In addition, loading of the ECG amplifier by the relatively low impedance of the defibrillator output must be prevented. Moroever, it is desirable to protect the implanted defibrillator from external defibrillator pulses.
When a pacer is to be employed with an implantable defibrillator, it is similarly desirable to protect the pacer from the defibrillator pulses. Moreover, in certain other arrangements, it is desirable to provide additional protection and interface of the pacer circuitry, as will be discussed below.